A nurse is assisting with the care of a client in the emergency department and reports severe radiating chest pain and shortness of breath. The client appears restless, frightened, and slightly cyanotic. The provider prescribes oxygen by nasal cannula at 4 L/min stat, cardiac enzyme levels. IV fluids, and an ECG/EKG. Which of the following actions should the nurse take first?

A. Inserting the IV catheter is necessary for fluids and medications but is not the immediate priority. B. Obtaining blood samples for cardiac enzymes is important for diagnosis, but treatment of hypoxemia takes priority. C. An ECG is essential for identifying ischemic changes, but restoring oxygenation is more urgent. D. According to the ABCs (airway, breathing, circulation), oxygen therapy should be initiated first to improve oxygenation and reduce hypoxia in a client with chest pain and cyanosis.